1. Field of Invention
The invention relates to packing media and particularly to plastic trickling filter media for biological filters used for the purification of polluted liquids and other effluents.
2. Description of the Prior Art
Heretofore, various forms of media have been proposed for packing both liquid-gas contact towers, biological filter vessels and the like through which the liquid percolates by gravity. In addition to packings made up of stones, rocks, clinker, granite chips there has been previously proposed rigid elements made up of alternately arranged flat and corrugated sheets, spaced corrugated sheets, tubes divided in a honey comb type structure and individual molded elements of various shapes with the aim of providing a large area of exchange contact surfaces.
British Pat. No. 1,275,116 discloses a rigid cylindrical element having a perforated wall and spaced groups of angularly spaced radially extending ribs. U.S. Pat. No. 3,506,248 discloses both cylindrical and polygonal shape plastic elements with a plurality of coaxially aligned spaced parallel walls of different axial length interconnected by ribs or fins. Hence the opposite end portions of the elements have the form of either an inverse truncated cone or polygonal pyramid.
In U.S. Pat. No. 3,365,180 there is disclosed a tubular packing element with elongated, generally ellipsoidal, angularly offset open ends between which extends a single tapered wall surrounding a central opening of irregular shape. The single tapered wall has four side portions each tapered in the opposite direction from the adjacent side portion.
Another packing media is disclosed in U.S. Pat. No. 3,475,012 comprising a plurality of plastic sheets each of which have a plurality of hollow protuberances molded therein to the shape of a frustum of either a cone or pyramid. The sheets are spaced and arranged vertically so the hollow protuberances extend horizontally or transverse to the vertical plane of the tower.
Applicant is also aware of another plastic packing element disclosed in U.S. Pat. No. 3,914,351 and sold under the trade name "Cascade Miniring" by Mass Transfer Limited of Westmoreland, England. Unlike the applicant's element the "Cascade Miniring" has but a single outer perforated tapered wall extending between large and small end diameters of the element.
Applicant's invention is a significant improvement over known prior art media in that a packing thereof provides 40 to 50% of more surface area per cubic unit of measurement than the conventional media which is known to be between 26-29 square feet per cubic foot or 85.3 - 95.1 square meters per cubic meter, and in which the majority of the surfaces are inclined and lie in a diagonal position relative to the axis of the vessel.